Glass with reinforced layer and preparation method thereof

ABSTRACT

A glass with a reinforced layer is provided, including a glass body and the reinforced layer formed in a surface of the glass body. The compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The compressive stress curve of the reinforced layer has an inflection point. The gradient of a first curve section in front of the inflection point is greater than the gradient of a second curve section behind the inflection point. The overall refractive index of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The refractive index curve of the reinforced layer has at least two inflection points. Furthermore, a method for preparing the glass with a reinforced layer is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. application Ser. No. 15/801,311 filed on Nov. 1, 2017, which is a Continuation Application of PCT Application No. PCT/CN2016/086517 filed on Jun. 21, 2016, which claims the benefit of Chinese Patent Application No. 201610428115.X filed on Jun. 16, 2016. All the above are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present application relates to the technical field of glass manufacturing, and particularly to glass with a reinforced layer, and a preparation method thereof.

BACKGROUND

Chemically reinforced glass is currently widely used in mobile phones, media players and other terminals, due to its high transparency, high strength and abrasion resistance. The high strength of the chemically reinforced glass is achieved by ion exchange. The principle is that small ions in the glass can be replaced by the large ions in a molten salt bath at high temperatures, and the large ions are tightly piled up on the glass surface to create a strong compressive stress after replacement, whereby a high strength is exhibited.

However, during the ion exchange process, the large ions in the molten salt bath are diluted with increasing number of small ions exchanged out. If the same molten salt bath is still used, the compressive stress of the glass will be reduced. In order to solve such a technical problem, a solution is employed at present, in which the ion exchange is achieved with two different molten salt baths. The glass is initially subjected to ion exchange in a first molten salt bath, and then taken out, cooled and dried after the large ions in the first molten salt bath are diluted to some degree, preheated again, and then subjected to ion exchange in a second molten salt bath, where the concentration of the large ions in the second molten salt bath is greater than that of the large ions in the diluted first molten salt bath. The stress distribution in the compressive stress layer formed by treatment with such molten salt baths is that the compressive stress layer does not change much in the depth direction and the compressive stress layer has a continuous monolayer structure. The concentration of the large ions exchanged varies over the depth of the glass in such a pattern that the concentration of the large ions is high merely at a position close to the glass surface and declines sharply inside the glass. This will necessarily result in uneven strength distribution of the compressive stress layer of the reinforced glass finally formed.

In short, so far, the stress distribution or the concentration of the exchanged ions in the monolayer compressive stress layer formed in the glass surface through physical or chemical tempering or through one or more tempering processes decreases progressively along the direction from the glass surface to the interior of the glass, resulting in a compressive stress layer that does not change much in the depth direction. As a result, the overall strength of the glass is failed to be improved.

SUMMARY

Accordingly, the present application provides glass with a reinforced layer and a preparation method thereof, so as to enhance the internal composite compressive stress of the glass, thereby achieving an increased overall strength of the glass.

Glass with a reinforced layer comprises a glass body and the reinforced layer formed in a surface of the glass body. The compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The compressive stress curve of the reinforced layer has an inflection point, and the gradient of a first curve section in front of the inflection point is greater than the gradient of a second curve section behind the inflection point. The overall refractive index of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body, and the refractive index curve of the reinforced layer has at least two inflection points.

Preferably, the reinforced layer contains metal ions exchanged into the reinforced layer, and the molar concentration of the metal ions exchanged into the reinforced layer trends to gradually decrease non-linearly in a direction running from the surface of the glass body to the interior of the glass body.

Preferably, a first inflection point on the refractive index curve of the reinforced layer is located at a position between 5-30 um in the direction running from the surface of the glass body to the interior of the glass body, and located at a position reaching 4-50% of a total ion-exchange depth in the direction running from the surface of the glass body to the interior of the glass body. A second inflection point is located at a position between 10-50 um in the direction running from the surface of the glass body to the interior of the glass body, and located at a position reaching 8-85% of the total ion-exchange depth in the direction running from the surface of the glass body to the interior of the glass body. A maximum value of the refractive index presents at an outermost surface of the glass body, and the difference between the maximum value and the refractive index of the glass body is not higher than 0.1.

Preferably, the total ion-exchange depth is not less than 60 gm, and the compressive stress at the surface of the glass body is not less than 600 Mpa

Preferably, the reinforced glass has a thickness of 0.1-10 mm.

A method for preparing a glass with a reinforced layer comprises:

Step A: providing glass, preheating the glass in a temperature environment lower than that of a molten salt bath, and subjecting the preheated glass to a first ion exchange process for a time T₁ in the molten salt bath, to form a reinforced layer L₁ in a surface of the glass;

Step B: thermally processing the glass formed with the reinforced layer L₁ for a time t_(h) that is from above 20 min to 30 min in an temperature environment of T_(h) ranging from 390° C. to a temperature that is 10° C. below an annealing point of the glass, to allow the ingredient of the molten salt bath adhered to the glass surface to further undergo ion exchange with the glass, and allow the reinforced layer L₁ to expand toward the interior of the glass by at least 3 gm, wherein the distribution of the ions exchanged into the reinforced layer L₁ is diluted, and a reinforced layer L₂ is formed by integrating the ions newly exchanged in this step; and

Step C: cooling the glass having the reinforced layer L₂ to the temperature of the molten salt bath, and subjecting the glass to a second ion exchange process in the same molten salt bath in Step A; or rinsing the glass, and then subjecting the glass to a second ion exchange process in a molten salt bath different from that in Step A, where the time for the second ion exchange process is t₂, the temperature for the second ion exchange process is T₂; and a reinforced layer L₃ is formed on the surface of the glass having the reinforced layer L₂ by ion exchange, the reinforced layer L₂ inside the glass undergoes ion exchange with the ions inside and peripheral to the glass and expands continuously toward the interior and periphery of the glass along a direction of the concentration difference, the reinforced layer L₃ expands at a rate higher than that of the reinforced layer L₂, and after full ion exchange reaction, the reinforced layer L₃ is overlapped with the reinforced layer L₂, to form a reinforced layer,

where the time and temperature for the second ion exchange process in Step C and the time and temperature for the thermal processing in Step B satisfy T₂×t₂<T_(h)×(t_(h)/2).

Preferably, the glass having the reinforced layer L₁ obtained in Step A is taken out, cooled, and rinsed, to remove the ingredient of the molten salt bath adhered to the glass surface in Step A completely, and then the rinsed glass having the reinforced layer L₁ is used in the process of Step B.

Preferably, Steps B-C are repeated, until a satisfactory reinforced layer is formed in the glass.

Preferably, the temperature of the molten salt bath is 350-550° C. during the first and second ion exchange process.

Preferably, the glass is alkaline silicate glass comprising 15-72 wt % of SiO₂; 10-43 wt % of Al₂O₃ or/and P₂O₅ in total; 8-33 wt % of alkaline metal oxides in total; and less than 15 wt % of other oxides.

Preferably, a maximum value of the refractive index presents at an outermost surface of the glass body, and a difference between the maximum value and the refractive index of the glass body is not higher than 0.1

Compared with the prior art, the present application has the following advantages.

In the preparation method according to the present application, a condition is established between the time and temperature for the thermal processing in Step B and the time and temperature for the second ion exchange process in Step C: T₂×t₂<T_(h)×(t_(h)/2). Glass with a reinforced layer having characteristics different from those of the reinforced glass in the prior art is obtained through the preparation process where the condition is satisfied. Firstly, the refractive index of the glass has unique features. That is, the refractive index of the reinforced layer trends to decrease non-linearly, on the whole, from the surface of the glass body to the interior of the glass body, and the refractive index curve of the reinforced layer has at least two inflection points. Secondly, the compressive stress distribution of the glass has its own features. That is, the compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body; and the compressive stress curve of the reinforced layer has an inflection point, the gradient of a first curve section in front of the inflection point is greater than a second curve section behind the inflection point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows distribution curves of K ions in molar percentage in reinforced layers obtained in different steps in an embodiment of the present application.

FIG. 2 shows distribution curves of the refractive index tested with polarized lights in X and Y directions of glass with a reinforced layer obtained in an embodiment of the present application.

FIG. 3 shows a compressive stress distribution curve of glass with a reinforced layer obtained in an embodiment of the present application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To make the objects, technical solutions and advantages of the present application clearer, the present application will now be described in further detail by way of examples with reference to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The present application provides a method for preparing glass with a reinforced layer, which comprises the following steps.

Step A: Glass is provided, preheated in a temperature environment lower than that of a molten salt bath, and subjected to a first ion exchange process for a time T₁ in the molten salt bath, to form a reinforced layer L₁ in a surface of the glass.

Step B: The glass formed with the reinforced layer L₁ is thermally processed for a time t_(h) that is from above 20 min to 30 min in an temperature environment of T_(h) ranging from 390° C. to a temperature that is 10° C. below an annealing point of the glass, to allow the ingredient of the molten salt bath adhered to the glass surface to further undergo ion exchange with the glass, and allow the reinforced layer L₁ to expand toward the interior of the glass by at least 3 μm, where the distribution of the ions exchanged into the reinforced layer L₁ is diluted, and a reinforced layer L₂ is formed by integrating the ions newly exchanged in this step.

Step C: The glass having the reinforced layer L₂ is cooled to the temperature of the molten salt bath, and the glass is subjected to a second ion exchange process in the same molten salt bath in Step A; or the glass is rinsed, and then subjected to a second ion exchange process in a molten salt bath different from that in Step A, where the time for the second ion exchange process is t₂, and the temperature for the second ion exchange process is T₂; and a reinforced layer L₃ is formed on the surface of the glass having the reinforced layer L₂ by ion exchange, the reinforced layer L₂ inside the glass undergoes ion exchange with the ions inside and peripheral to the glass and expands continuously toward the interior and periphery of the glass along a direction of the concentration difference, the reinforced layer L₃ expands at a rate higher than that of the reinforced layer L₂, and after full ion exchange reaction, the reinforced layer L₃ is overlapped with the reinforced layer L₂, to form a reinforced layer; and the time and temperature for the second ion exchange process in Step C and the time and temperature for the thermal processing in Step B satisfy T₂×t₂<T_(h)×(t_(h)/2).

Optionally, the glass having the reinforced layer L₁ obtained in Step A is taken out, cooled, and rinsed, to remove the ingredient of the molten salt bath adhered to the glass surface in Step A completely, and then the rinsed glass having the reinforced layer L₁ is used in the process of Step B. The rinsing process before Step B is provided for preventing the influence on the purity and the stress intensity of the final reinforced layer by the ingredient of the molten salt bath that is reacted and attached to the glass surface during the thermal processing of Step B.

Optionally, Steps B-C are repeated, until a reinforced layer meeting the compressive stress and depth requirements is formed on the glass.

During the preparation process, the temperature of the molten salt bath is 350-550° C.

By means of the preparation method, glass with a reinforced layer is obtained, which comprises a glass body and a reinforced layer formed in a surface of the glass body. The compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The compressive stress curve of the reinforced layer has an inflection point, and the gradient of a first curve section in front of the inflection point is greater than the gradient of a second curve section behind the inflection point. The overall refractive index of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body, and the refractive index curve of the reinforced layer has at least two inflection points.

In the glass with a reinforced layer, the reinforced layer contains metal ions exchanged into the reinforced layer, and the molar concentration of the metal ions exchanged into the reinforced layer trends to gradually decrease non-linearly in a direction running from the surface of the glass body to the interior of the glass body.

In the glass with a reinforced layer, a first inflection point on the refractive index curve of the reinforced layer is located at a position between 5-30 um in the direction running from the surface of the glass body to the interior of the glass body, and located at a position reaching 4-50% of a total ion-exchange depth in the direction running from the surface of the glass body to the interior of the glass body. A second inflection point is located at a position between 10-50 um in the direction running from the surface of the glass body to the interior of the glass body, and located at a position reaching 8-85% of the total ion-exchange depth in the direction running from the surface of the glass body to the interior of the glass body. A maximum value of the refractive index presents at an outermost surface of the glass body, and the difference between the maximum value and the refractive index of the glass body is not higher than 0.1.

In the glass with a reinforced layer, the total ion-exchange depth is not less than 60 μm, and the compressive stress at the surface of the glass body is not less than 600 Mpa.

The glass with a reinforced layer has a thickness of 0.1-10 mm.

The glass for forming the reinforced layer is alkaline silicate glass comprising 15-72 wt % of SiO₂; 10-43 wt % of Al₂O₃ or/and P₂O₅ in total; 8-33 wt % of alkaline metal oxides (Li₂O or/and Na₂O or/and K₂O) in total; and less than 15 wt % of other oxides.

EXAMPLE

Molten salt bath: 100% KNO₃;

The time period and temperature for the first ion exchange process and the time period and temperature for the second ion exchange process satisfy: T₂×t₂<T_(h)×(t_(h)/2).

The temperature and time period for the first ion exchange process: 430° C., 3.5 h;

The time period and temperature for the thermal processing: 530° C., 2 h;

The temperature and time period for the second ion exchange process: 430° C., 1 h;

Component of the glass to be reinforced:

Component Content (wt %) SiO₂ 61 Al₂O₃ 17.3 Fe₂O₃ 0.5 CaO 0.2 MgO 3.2 K₂O 1.8 Na₂O 15.5 TiO₂ 0.5

As shown in FIG. 1 , after Step A is performed, a reinforced layer L₁ is formed on the surface and inside the glass, and the distribution of the exchanged ions K in molar percentage is as shown by the curve of the reinforced layer L₁ in FIG. 1 . After Step B is performed, the glass is placed in an environment where no source of ions for exchange is available, the K ions inside the reinforced layer L₁ can only be further exchanged with Na inside the glass, and the distribution of K expands toward the interior of the glass on one hand, and is diluted on the other hand, thus forming a reinforced layer L₂. FIG. 1 shows a distribution curve of the exchanged K ions in molar percentage in the reinforced layer L₂. After Step C is performed, the reinforced layer L₂ is redistributed again, and thus expands further toward the interior of the glass on one hand, and is further diluted on the other hand. As new K ions are exchanged into the glass from the molten salt bath containing the source of ions for exchange, the K ions newly entered the glass moves at a rate much faster than that of the existing reinforced layer L₂ in the glass, and is combined with the reinforced layer L₂, to form a reinforced layer L₃. FIG. 1 shows a distribution curve of the exchanged K ions in molar percentage in the reinforced layer L₃.

Moreover, if a rinsing process is additionally added before Step B, and the same conditions are maintained in the subsequent procedure steps, the resulting outcome can be slightly reflected in the curve of the reinforced layer L₂ and the curve of the reinforced layer L₃ obtained in Steps B and C respectively. The curve of the reinforced layer L₂ obtained in Step B becomes slightly flattened, and the gradient will be smaller. The curve of the reinforced layer L₃ obtained in Step C also has the same characteristics of change. The change in the curve of the reinforced layer L₃ is very small, because a large amount of K ions newly entered the glass from the molten salt bath in Step C, and the molar concentration of these K ions masks the changes that present in step B. Therefore, although a rinsing process is added, the characteristics of the finally obtained reinforced layer L₃ are unchanged. The rising process is added for the purpose of removing the remaining ingredient of the molten salt bath on the glass surface obtained after Step A before it entering the thermal processing process (e.g. baking) of Step B, so as to avoid the destruction on the purity of the finally obtained reinforced layer L₃ by the remaining ingredient of the molten salt bath that is reacted upon heating and attached to the glass surface during the thermal processing of Step B, and avoid the contamination of the molten salt bath used in Step C arising therefrom.

As shown in FIG. 2 , the refractive index of the reinforced glass having the reinforced layer L₃ prepared through the method above has the following characteristics.

When the stress is measured by an optical method, the refractive index tested with two polarized lights are obtained, and then the surface stress is calculated according to the difference therebetween and according to various constants and variables of the glass and the measuring instrument. The test method is within the prior art of the industry, and will not be described again in the present application. FIG. 2 shows distribution curves of the refractive index tested with polarized lights in X and Y directions of glass with a reinforced layer obtained in this example. Two refractive index distribution curves are correspondingly obtained. Apparently, FIG. 2 obviously shows that the refractive index of the reinforced layer L₃ trends to decreases non-linearly, on the whole, from the surface of the glass body to the interior of the glass body, and the refractive index curve of the reinforced layer L₃ has at least two inflection points.

As shown in FIG. 3 , the compressive stress of the reinforced layer L₃ has the following characteristics.

It is known in the art that the compressive stress is obtained through calculation based on the values of the refractive indices measured at selected points and on other constants and variables introduced, and then fitting a final curve. The method of fitting a curve is within the prior art of the industry, and will not be described again in the present application. Apparently, FIG. 3 obviously shows that the compressive stress of the reinforced layer L₃ trends to decrease non-linearly from the surface of the glass body to the interior of the glass body; and the compressive stress curve of the reinforced layer L₃ has an inflection point, and the gradient of a first curve section in front of the inflection point is greater than a second curve section behind the inflection point.

Compared with the prior art, the present application has the following advantages.

In the preparation method according to the present application, a condition is established between the time and temperature for the thermal processing in Step B and the time and temperature for the second ion exchange process in Step C: T₂×t₂<T_(h)×(t_(h)/2). Glass with a reinforced layer having characteristics different from those of the reinforced glass in the prior art is obtained through the preparation process where the condition is satisfied. Firstly, the refractive index of the glass has unique features. That is, the refractive index of the reinforced layer trends to decrease non-linearly, on the whole, from the surface of the glass body to the interior of the glass body, and the refractive index curve of the reinforced layer has at least two inflection points. Secondly, the compressive stress distribution of the glass has its own features. That is, the compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body; and the compressive stress curve of the reinforced layer has an inflection point, the gradient of a first curve section in front of the inflection point is greater than a second curve section behind the inflection point.

The foregoing description is merely illustrative of the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made without departing from the spirit and principles of the application are encompassed in the protection scope of the present application. 

The invention claimed is:
 1. A method for preparing a glass with a reinforced layer, comprising: Step A: providing glass which comprises: 61 wt % of SiO₂, 17.3 wt % of Al₂O₃, 0.5 wt % of Fe₂O₃, 0.2 wt % of CaO, 3.2 wt % of MgO, 1.8 wt % K₂O, 15.5 wt % of Na₂O and 0.5 wt % of TiO₂, preheating the glass in a temperature environment lower than that of a molten salt bath, and subjecting the preheated glass to a first ion exchange process in the molten salt bath, to form a reinforced layer L₁ in a surface of the glass, wherein the molten salt bath is 100% KNO₃ and a temperature and time period for the first ion exchange process are 430° C., 3.5 hours; Step B: thermally processing the glass formed with the reinforced layer L₁ for a time period t_(h), to allow ingredient of the molten salt bath adhered to the glass surface to further undergo ion exchange with the glass, and allow the reinforced layer L₁ to extend into the interior of the glass by at least 3 gm, wherein a distribution of ions exchanged from the molten salt bath in step A into the reinforced layer L₁ is diluted, and a reinforced layer L₂ is formed by integrating ions which are exchanged in this step B with the ions which are exchanged in step A and then diluted in step B; wherein a time period and temperature for the thermal processing are 530° C., 2 hours; and Step C: cooling the glass having the reinforced layer L₂ to the temperature of the molten salt bath, and subjecting the glass to a second ion exchange process in the same molten salt bath in Step A; or rinsing the glass, and then subjecting the glass to a second ion exchange process in a molten salt bath different from that in Step A, wherein a temperature and time period for the second ion exchange process are 430° C., 1 hour; and a reinforced layer L₃ is formed on the surface of the glass having the reinforced layer L₂ by ion exchange, the reinforced layer L₂ inside the glass undergoes ion exchange with the ions inside and peripheral to the glass and extends continuously into the interior and a periphery of the glass along a direction of the concentration difference, the reinforced layer L₃ extends at a rate higher than that of the reinforced layer L₂, and after full ion exchange reaction, the reinforced layer L₃ is overlapped with the reinforced layer L₂, to form a reinforced layer; wherein an overall refractive index of the reinforced layer trends to decrease non-linearly from the surface of the glass to an interior of the glass; and the refractive index curve of the reinforced layer has at least two inflection points; a maximum value of the refractive index presents at an outermost surface of the glass, and a difference between the maximum value and the refractive index of the glass is not higher than 0.1; a compressive stress curve of the reinforced layer has an inflection point, a gradient of a first curve section in front of the inflection point is greater than a second curve section behind the inflection point.
 2. The preparation method according to claim 1, wherein the glass having the reinforced layer L₁ obtained in Step A is taken out, cooled, and rinsed, to remove the ingredient of the molten salt bath adhered to the glass surface in Step A completely, and then the rinsed glass having the reinforced layer L₁ is used in the process of Step B.
 3. The preparation method according to claim 1, wherein Steps B-C are repeated, until the reinforced layer is formed on the glass. 